Collagen fibril organization in chicken and porcine skeletal muscle perimysium under applied tension and compression

Skeletal muscle extracellular matrix structure under applied deformation observed using second harmonic generation microscopy

The mechanical and structural properties of passive skeletal muscle are important for musculoskeletal models in impact biomechanics, rehabilitation engineering and surgical simulation. Passive properties of skeletal muscle depend strongly on the architecture of the extracellular matrix (ECM), but the structure of ECM and its realignment under applied deformation remain poorly understood. We apply second harmonic generation (SHG) microscopy to study muscle ECM in intact muscle samples both under deformation and in the undeformed state. A method for regional relocation was developed, so that the same ECM segment could be viewed before and after applying deformations. Skeletal muscle ECM was viewed at multiple scales and in three states: undeformed, under compression and under tension. Results show that second harmonic generation microscopy provides substantial detail of skeletal muscle ECM over a wide range of length scales, especially the perimysium structure. We present images of individual portions of skeletal muscle ECM both undeformed and subjected to tensile/compressive deformation. We also present data showing the response of the perimysium to a partial thickness cut applied to a section under tensile deformation. STATEMENT OF SIGNIFICANCE: Second Harmonic Generation (SHG) microscopy is an imaging technique which takes advantage of a non-linear and coherent frequency doubling optical effect that is present in a small number of biological molecules, primarily collagen Type I, II and myosin. Collagen I is the most abundant collagen type in skeletal muscle, making SHG a promising option for visualisation of the skeletal muscle extracellular matrix (ECM). SHG microscopy does not require fixing or staining. This short communication presents the application of SHG microscopy to skeletal muscle ECM to improve our understanding of how collagen fibres reorganise under applied tensile and compression, including microscopic observations of collagen fibre reorganisation for intact samples by using a method to re-identify specific regions in repeated deformation tests.

Alignment, cross linking, and beyond: a collagen architect's guide to the skeletal muscle extracellular matrix

The muscle extracellular matrix (ECM) forms a complex network of collagens, proteoglycans, and other proteins that produce a favorable environment for muscle regeneration, protect the sarcolemma from contraction-induced damage, and provide a pathway for the lateral transmission of contractile force. In each of these functions, the structure and organization of the muscle ECM play an important role. Many aspects of collagen architecture, including collagen alignment, cross linking, and packing density affect the regenerative capacity, passive mechanical properties, and contractile force transmission pathways of skeletal muscle. The balance between fortifying the muscle ECM and maintaining ECM turnover and compliance is highly dependent on the integrated organization, or architecture, of the muscle matrix, especially related to collagen. While muscle ECM remodeling patterns in response to exercise and disease are similar, in that collagen synthesis can increase in both cases, one outcome leads to a stronger muscle and the other leads to fibrosis. In this review, we provide a comprehensive analysis of the architectural features of each layer of muscle ECM: epimysium, perimysium, and endomysium. Further, we detail the importance of muscle ECM architecture to biomechanical function in the context of exercise or fibrosis, including disease, injury, and aging. We describe how collagen architecture is linked to active and passive muscle biomechanics and which architectural features are acutely dynamic and adapt over time. Future studies should investigate the significance of collagen architecture in muscle stiffness, ECM turnover, and lateral force transmission in the context of health and fibrosis.

Aponeurosis structure-function properties: Evidence of heterogeneity and implications for muscle function

Aponeurosis is a sheath-like connective tissue that aids in force transmission from muscle to tendon and can be found throughout the musculoskeletal system. The key role of aponeurosis in muscle-tendon unit mechanics is clouded by a lack of understanding of aponeurosis structure-function properties. This work aimed to determine the heterogeneous material properties of porcine triceps brachii aponeurosis tissue with materials testing and evaluate heterogeneous aponeurosis microstructure with scanning electron microscopy. We found that aponeurosis may exhibit more microstructural collagen waviness in the insertion region (near the tendon) compared to the transition region (near the muscle midbelly) (1.20 versus 1.12, p = 0.055), which and a less stiff stress-strain response in the insertion versus transition regions (p < 0.05). We also showed that different assumptions of aponeurosis heterogeneity, specifically variations in elastic modulus with location can alter the stiffness (by more than 10x) and strain (by approximately 10% muscle fiber strain) of a finite element model of muscle and aponeurosis. Collectively, these results suggest that aponeurosis heterogeneity could be due to variations in tissue microstructure and that different approaches to modeling tissue heterogeneity alters the behavior of computational models of muscle-tendon units. STATEMENT OF SIGNIFICANCE: Aponeurosis is a connective tissue found in many muscle tendon units that aids in force transmission, yet little is known about the specific material properties of aponeurosis. This work aimed to determine how the properties of aponeurosis tissue varied with location. We found that aponeurosis exhibits more microstructural waviness near the tendon compared to near the muscle midbelly, which was associated with differences in tissue stiffness. We also showed that different variations in aponeurosis modulus (stiffness) can alter the stiffness and stretch of a computer model of muscle tissue. These results show that assuming uniform aponeurosis structure and modulus, which is common, may lead to inaccurate models of the musculoskeletal system.

In vivoestimation of anisotropic mechanical properties of the gastrocnemius during functional loading with MR elastography

Objective.In vivoimaging assessments of skeletal muscle structure and function allow for longitudinal quantification of tissue health. Magnetic resonance elastography (MRE) non-invasively quantifies tissue mechanical properties, allowing for evaluation of skeletal muscle biomechanics in response to loading, creating a better understanding of muscle functional health.Approach. In this study, we analyze the anisotropic mechanical response of calf muscles using MRE with a transversely isotropic, nonlinear inversion algorithm (TI-NLI) to investigate the role of muscle fiber stiffening under load. We estimate anisotropic material parameters including fiber shear stiffness (μ1), substrate shear stiffness (μ2), shear anisotropy (ϕ), and tensile anisotropy (ζ) of the gastrocnemius muscle in response to both passive and active tension.Main results. In passive tension, we found a significant increase inμ1,ϕ,andζwith increasing muscle length. While in active tension, we observed increasingμ2and decreasingϕandζduring active dorsiflexion and plantarflexion-indicating less anisotropy-with greater effects when the muscles act as agonist.Significance. The study demonstrates the ability of this anisotropic MRE method to capture the multifaceted mechanical response of skeletal muscle to tissue loading from muscle lengthening and contraction.

miRNA-seq analysis in skeletal muscle of chicken and function exploration of miR-24-3p

The regulation of skeletal muscle growth and development in chicken is complex. MicroRNAs (miRNAs) have been found to play an important role in the process, and more research is needed to further understand the regulatory mechanism of miRNAs. In this study, leg muscles of Jinghai yellow chickens at 300 d with low body weight (slow-growing group) and high body weight (fast-growing group) were collected for miRNA sequencing (miRNA-seq) and Bioinformatics analysis revealed 12 differentially expressed miRNAs (DEMs) between the two groups. We predicted 150 target genes for the DEMs, and GO and KEGG pathway analysis showed the target genes of miR-24-3p and novel_miR_133 were most enriched in the terms related to growth and development. Moreover, networks of DEMs and target genes showed that miR-24-3p and novel_miR_133 were the 2 core miRNAs. Hence, miR-24-3p was selected for further functional exploration in chicken primary myoblasts (CPMs) with molecular biology technologies including qPCR, cell counting kit-8 (CCK-8), 5-ethynyl-2'-deoxyuridine (EdU) and immunofluorescence. When proliferating CPMs were transfected with miR-24-3p mimic, the expression of cyclin dependent kinase inhibitor 1A (P21) was up-regulated and both CCK-8 and EdU assays showed that the proliferation of CPMs was inhibited. However, when the inhibitor was transfected into the proliferating CPMs, the opposite results were found. In differentiated CPMs, transfection with miR-24-3p mimic resulted in up regulation of MYOD, MYOG and MYHC after 48 h. Myotube areas also increased significantly compared to the mimic negative control (NC) group. When treated with inhibitor, differentiation CPMs produced the opposite effects. Overall, we revealed 2 miRNAs (novel_miR_133 and miR-24-3p) significantly related with growth and development and further proved that miR-24-3p could suppress the proliferation and promote differentiation of CPMs. The results would facilitate understanding the effects of miRNAs on the growth and development of chickens at the post-transcriptional level and could also have an important guiding role in yellow-feathered chicken breeding.

On multiscale tension-compression asymmetry in skeletal muscle

Skeletal muscle tissue shows a clear asymmetry with regard to the passive stresses under tensile and compressive deformation, referred to as tension-compression asymmetry (TCA). The present study is the first one reporting on TCA at different length scales, associated with muscle tissue and muscle fibres, respectively. This allows for the first time the comparison of TCA between the tissue and one of its individual components, and thus to identify the length scale at which this phenomenon originates. Not only the passive stress-stretch characteristics were recorded, but also the volume changes during the axial tension and compression experiments. The study reveals clear differences in the characteristics of TCA between fibres and tissue. At tissue level TCA increases non-linearly with increasing deformation and the ratio of tensile to compressive stresses at the same magnitude of strain reaches a value of approximately 130 at 13.5% deformation. At fibre level instead it initially drops to a value of 6 and then rises again to a TCA of 14. At a deformation of 13.5%, the tensile stress is about 6 times higher. Thus, TCA is about 22 times more expressed at tissue than fibre scale. Moreover, the analysis of volume changes revealed little compressibility at tissue scale whereas at fibre level, especially under compressive stress, the volume decreases significantly. The data collected in this study suggests that the extracellular matrix has a distinct role in amplifying the TCA, and leads to more incompressible tissue behaviour. STATEMENT OF SIGNIFICANCE: This article analyses and compares for the first time the tension-compression asymmetry (TCA) displayed by skeletal muscle at tissue and fibre scale. In addition, the volume changes of tissue and fibre specimens with application of passive tensile and compressive loads are studied. The study identifies a key role of the extracellular matrix in establishing the mechanical response of skeletal muscle tissue: It contributes significantly to the passive stress, it is responsible for the major part of tissue-scale TCA and, most probably, prevents/balances the volume changes of muscle fibres during deformation. These new results thus shed light on the origin of TCA and provide new information to be used in microstructure-based approaches to model and simulate skeletal muscle tissue.

Predicting muscle tissue response from calibrated component models and histology-based finite element models

Skeletal muscle is an anisotropic soft biological tissue composed of muscle fibres embedded in a structurally complex, hierarchically organised extracellular matrix. In a recent work (Kuravi et al., 2021) we have developed 3D finite element models from series of histological sections. Moreover, based on decellularisation of fresh tissue samples, a novel set of experimental data on the direction dependent mechanical properties of collagenous ECM was established (Kohn et al., 2021). Together with existing information on the material properties of single muscle fibres, the combination of these techniques allows computing predictions of the composite tissue response. To this end, an inverse finite element procedure is proposed in the present work to calibrate a constitutive model of the extracellular matrix, and supplementary biaxial tensile tests on fresh and decellularised tissues are performed for model validation. The results of this rigorously predictive and thus unforgiving strategy suggest that the prediction of the tissue response from the individual characteristics of muscle cells and decellularised tissue is only possible within clear limits. While orders of magnitude are well matched, and the qualitative behaviour in a wide range of load cases is largely captured, the existing deviations point at potentially missing components of the model and highlight the incomplete experimental information in bottom-up multiscale approaches to model skeletal muscle tissue.

3D finite element models from serial section histology of skeletal muscle tissue - The role of micro-architecture on mechanical behaviour

In this contribution we create three-dimensional (3D) finite element models from a series of histological sections of porcine skeletal muscle tissue. Image registration is performed on the stained sections by affinely aligning them using auxiliary markers, followed by image segmentation to determine muscle fibres and the extracellular matrix in each section, with particular regard to the continuity of the fibres through the stack. With this information, 3D virtual tissue samples are reconstructed, discretised, and associated with appropriate non-linear elastic anisotropic material models. While the gross anatomy is directly obtained from the images, the local directions of anisotropy were determined by the use of an analogy with steady state diffusion. The influence of the number of histological sections considered for reconstruction on the numerically simulated mechanical response of the virtual tissue samples is then studied. The results show that muscle tissue is fairly heterogeneous along the fascicles, and that transverse isotropy is inadequate in describing their material symmetry at the typical length scale of a fascicle. Numerical simulations of different load cases suggest that ignoring the undulations of fibres and their non-uniform cross-sections only moderately affects the passive response of the tissue in tensile and compressive modes, but can become crucial when predicting the response to generic loads and activation.

Investigating Passive Muscle Mechanics With Biaxial Stretch

Introduction

The passive stiffness of skeletal muscle can drastically affect muscle function in vivo, such as the case for fibrotic tissue or patients with cerebral palsy. The two constituents of skeletal muscle that dominate passive stiffness are the intracellular protein titin and the collagenous extracellular matrix (ECM). However, efforts to correlate stiffness and measurements of specific muscle constituents have been mixed, and thus the complete mechanisms for changes to muscle stiffness remain unknown. We hypothesize that biaxial stretch can provide an improved approach to evaluating passive muscle stiffness.

Methods

We performed planar biaxial materials testing of passively stretched skeletal muscle and identified three previously published datasets of uniaxial materials testing. We developed and employed a constitutive model of passive skeletal muscle that includes aligned muscle fibers and dispersed ECM collagen fibers with a bimodal von Mises distribution. Parametric modeling studies and fits to experimental data (both biaxial and previously published) were completed.

Results

Biaxial data exhibited differences in time dependent behavior based on orientation (p < 0.0001), suggesting different mechanisms supporting load in the direction of muscle fibers (longitudinal) and in the perpendicular (transverse) directions. Model parametric studies and fits to experimental data exhibited the robustness of the model (<20% error) and how differences in tissue stiffness may not be observed in uniaxial longitudinal stretch, but are apparent in biaxial stretch.

Conclusion

This work presents novel materials testing data of passively stretched skeletal muscle and use of constitutive modeling and finite element analysis to explore the interaction between stiffness, constituent variability, and applied deformation in passive skeletal muscle. The results highlight the importance of biaxial stretch in evaluating muscle stiffness and in further considering the role of ECM collagen in modulating passive muscle stiffness.

Machine assisted classification of chicken, beef and mutton tissues using optical polarimetry and Bagging model

Optical polarimetry has been used to characterize muscle tissue samples of chicken, beef and mutton, exhibiting statistically significant (p <  0.01) differences in total depolarization and retardance of three tissue groups. Herein, the total depolarization and retardance were utilized to differentiate and classify the three tissue groups. Specifically, the Bagging classification algorithm was employed for this multi-class differentiation. The performance of the optical polarimetry in tandem with the Bagging model for machine-assisted classification of the three tissue groups was assessed in terms of a comprehensive set of evaluation metrics. The Bagging model correctly classified 47/48, 19/20 and 15/18, whereas the sensitivity (Sn = 97.9 %, 82.6 %, 100 %), specificity (Sp = 97.4 %, 98.4 %, 95.8 %), positive predictive values (PPV = 0.97, 0.95, 0.83) and negative predictive values (NPV = 0.97, 0.94, 1.0) were calculated for the chicken, beef and mutton tissue samples, respectively. This automatic classification of the three tissue samples indicates a novel application of the optical polarimetry in the meat industry.

The Effect of the Wooden Breast Fibrotic Myopathy in Broilers on Fibrillar Collagen Organization and Decorin-Collagen Binding

The wooden breast myopathy is identified by the palpation of a rigid pectoralis major muscle and results in myofiber necrosis and fibrosis in fast-growing, meat-type broilers. The fibrosis in wooden breast-affected muscle is characterized by the replacement of myofibers with extracellular matrix proteins, especially fibril-forming collagens. Studies have shown differences in collagen organization in fast-growing broiler lines, with tightly packed and highly aligned collagen organizations having a higher phenotypic incidence of wooden breast. The objective of the current study was to analyze collagen fibril organization further in two fast-growing broiler lines (Lines A and B) with incidence of wooden breast compared with a slower growing broiler Line C with no phenotypically detectable wooden breast. The small leucine-rich proteoglycan decorin was also studied for its interaction with collagen by immunogold detection. Decorin binds to fibrillar collagens and organizes their alignment and crosslinking, both of which will affect collagen functional properties. Key findings from the study showed that collagen shifts to larger diameter collagen fibril bundles with the wooden breast myopathy. Specifically, broilers affected with wooden breast from Line A had a more dramatic shift toward larger collagen fibril bundles compared with those affected from Line B. Wooden breast-affected Line A had collagen fibril bundles up to 8.4 µm, whereas Line B maximum size was 5.1 µm. Although decorin-collagen binding was not different overall in the wooden breast myopathy or broiler line, for small-diameter collagen fibril bundles, wooden breast-affected Line A had more decorin-collagen binding than wooden breast-affected Line B. Taken together, these data provide further evidence that multiple fibrotic myopathies are likely in fast-growing meat-type broilers.

Exploring the Pathological Role of Collagen in Paravertebral Muscle in the Progression of Idiopathic Scoliosis

BACKGROUND

Paravertebral muscle (PVM) is considered as a contributing factor of idiopathic scoliosis (IS); collagen is crucial for maintaining the mechanical properties of PVM, but only a few researches have described this field. In this study, we observed the muscle stiffness of PVM and the curvature of the spine by adjusting the content of collagen in PVM of rats and explored the role of collagen in the progression of IS.

METHODS

32 female Sprague Dawley rats were randomly divided into four groups: neutralizing antibody (NA) group (group 1), normal control group (group 2), IS group (group 3), and IS with NA group (group 4). TGF-β1 NA was injected into PVM in group 1 and group 4, while Normal saline in group 2 and group 3. The Cobb angle and muscle stiffness were measured before and after injection; the rats were sacrificed at one week after injection, and performed histological, Western Blot, and qRT-PCR examinations.

RESULTS

X-rays showed that scoliosis occurred in group 1 and relieved in group 4. The stiffness of PVM was decreased significantly on the convex side in group 1, while on the concave side in group 4. The expression of TGF-β1 and COL1 on the concave side in IS rats (group 3) was significantly increased than that in normal rats (group 2), the concentration of COL1 and COL3 in group 3 was significantly higher than that in group 2, and the addition of TGF-β1 NA significantly downregulated COL1 and COL3 in group 1 and group 4. The concentration of COL1 in convex PVM was negatively related to Cobb angle in group 1 and group 2, and in concave PVM was positively related to Cobb angle in group 3 and group 4. However, no significant correlation was found between COL3 and Cobb angle in group 3 and group 4.

CONCLUSIONS

Asymmetric biomechanical characteristics of PVM was an important etiological factor of IS, which was directly correlated with collagen, it could be adjusted by local intramuscular injecting of TGF-β1 NA, and finally had an effect on the shape of the spine.

The dual functions of flavor and antioxidant potential of porcine bone marrow extract (PBME)

To improve and confirm the dual functions of flavor and antioxidant potential of porcine bone marrow extract (PBME). Response surface methodology and Box-Behnken design was employed to optimize the conditions for enzymatic hydrolysis of PBME. The optimal hydrolysis conditions were: hydrolysis time, 3h; temperature, 55 °C; substrate concentration, 375g/L; and amount of enzyme, 0.4%. L₁₆(3⁵) orthogonal experimental was utilized to obtain the optimal Maillard reaction conditions for PBME and enzymatic hydrolysate of PBME (EH-PBME). The optimal conditions for PBME were: components, 4% glucose, 2% xylose, 1.5% Tyr, 1.5% Ala, and 4% VB₁; reaction time, 40 min; and reaction temperature, 115 °C. The optimal conditions for EH-PBME were: components, 2% glucose, 2% xylose, 3% Ala, and 5% VB₁; reaction time, 40 min; temperature, 110 °C. The antioxidant activities for PBME, EH-PBME, Maillard reaction products of PBME (MPRs A) and Maillard reaction products of EH-PBME (MPRs B) were 50%, 86%, 84% and 41% respectively. The content of taste-active substances and volatile compounds were also determined. Finally, PLSR was employed to evaluate the correlation between flavor compounds and sensory data.